[Pathology of cardiac lesions induced by radiofrequency ablation in an experimental model]

Radiofrequency catheter ablation is increasingly being used for the treatment of several tachyarrhythmias. The main aim of this paper is to describe the lesional pathology produced by this type of current. Fourteen Wistar rats (mean weight 300 g) were subjected to discharges of a 700 KHz, pure, unmodulated, sine-wave radiofrequency generator. Three rats, through open chests, received epicardial shocks and were immediately sacrificed ("acute" lesions). The remaining 11 rats received shocks through percutaneously plunged tungsten wires, and were sacrificed 1 to 4 weeks after the procedure ("chronic" lesions). Hearts were fixed in buffered (pH7) 10% formalin solution. Selected slices were stained with hematoxilin-eosin and Mallory trichrome. Other slices were fixed in 3% glutaraldehyde and post-fixed in osmium tetroxyde, dehydrated and included in Polybed 812. Ultrathin slices were stained with uranil acetate and lead citrate and examined in a JEOL JEM-100 C electronic microscope. "Acute" specimens showed small coagulation necrosis areas, well delimited by carbonization and hemorrhages. Neighbouring myocardium showed one o two rows of moderate cell lesions which consisted of cytoplasmic homogeneization and increased contracture bands. " Chronic" lesions showed granulation tissue with mononuclear infiltrates and neoformation vessels surrounding a central necrosis area. The older the lesion, the larger the number of fibroblasts and mature collagen tissue. Ultrastructural studies showed irreversible myocardial changes in the lesional borders, with cytosolic and myofibrillar edema, contracture bands and rupture of mitochondrial crests. Radiofrequency lesions are limited, shallow and with net borders, which makes them almost ideal for subendocardial ablation of small arrhythmogenic areas.